1. Field of the Invention
The present is broadly concerned with improved short length, high speed extrusion cooking devices of the type generally described in U.S. Pat. No. 5,694,833 equipped with peripheral dies allowing greater product throughputs while increasing product densities, cook values and moisture levels. More particularly, the invention pertains to such improved extrusion cookers, and corresponding methods, wherein a peripheral extrusion die is disposed across the extruder barrel outlet and has a series of extrusion outlet openings oriented transverse to the longitudinal axis of the barrel. The peripheral dies of the invention may be provided with individual, axially spaced apart series of die outlet openings (usually with different numbers of outlet openings in each series), or more preferably with a radially enlarged peripheral die having only a single series of die openings.
2. Description of the Prior Art
U.S. Pat. No. 5,694,833 (incorporated by reference herein) describes a significant breakthrough in the extruder art. Specifically, that patent discloses relatively short length extruders (having an L/D ratio of up to about 6) which are operated at high screw rotational speeds typically in excess of 500 rpm. It has been found that extruders of this type are capable of producing, at relatively high output rates, feed products of very high integrity. Moreover, such extruders can be produced at lower costs as compared with conventional cooking extruders.
Extruders of this type are heretofore have been equipped with conventional plate-type face dies bolted across the outlet end of the extruder barrel. Dies of this variety have a series of die outlet openings which are essentially parallel with the longitudinal axis of the extruder barrel. Face dies, while in widespread use, tend to restrict extruder throughputs. Furthermore, because such dies must withstand considerable pressure, they are normally relatively expensive.
It has also been known in the past to equip certain long-barrel extruders with so-called "peripheral" dies. Dies of this character have die outlet openings oriented transverse to the longitudinal axis of the extruder barrel. Generally speaking, peripheral dies have a tendency to adversely affect product quality, particularly where relatively dense extrudates are desired. Accordingly, peripheral dies have not achieved wide spread use in the extrusion art.